Faced with a new regulatory requirement to monitor freight car loading and unloading of hazardous materials, a paper mill in South Carolina could assign a worker to watch the entire loading/unloading process or monitor it remotely via video from the control room. The mill decided it wanted to add cameras.
But a plan to add the cameras to an existing wired network cost too much. A wireless system was found to be much less expensive and allows additional cameras to be placed where coax is not available. At the Emerson Exchange user group meeting last month in Dallas, Dan Blome, wireless solutions engineer, ProSoft Technology, addressed the challenge of how to choose an appropriate wireless technology, design a wireless network, choose and configure cameras, and test and troubleshoot a final installation.
The 2.4-GHz 802.11g/n spectrum offers three channels, but most process monitoring systems run on the 23-channel, 5-GHz 802.11 a/n spectrum, which offers rates up to 72 Mbps by bonding two adjacent channels — the n designation — and up to 144 Mbps by multiple streaming using multiple-input, multiple output (MIMO) antennas. "It's mainly only practical at 5 GHz due to channel count, but 5 GHz does have lower range due to its higher frequency," Blome said.
Designing the system requires basic site information, starting with the video server location (most designs place the server in the control room). Decide where antennas can be located using a plant layout. "You can use Google Earth to zoom in and determine the distances between the remote locations and the control room," Blome said. "Then verify that there are unbroken lines of sight between antenna locations."
Software tools help you use the distances between locations to calculate signal strengths and verify optimal data rates. "The weaker the signal, the less bandwidth," Blome said. "Make the bandwidth as high as possible." Design software helps you select antennas and cables.
Blome said that now is the time to decide camera numbers, frame rates and frame sizes (resolution) to determine the necessary data rate. Catching process information, where materials move at higher speeds than people walk, often requires 30 frames per second. The cameras themselves are similar, but vary in lens quality and pan/zoom capabilities. Choose the right camera for the job in each location. Be realistic — many process applications don't require high frame rates or resolutions.
The system should be clamped up temporarily and tested before components are permanently mounted. Even with good engineering and trials, expect some glitches. "There are some tools out there you can use for testing, and there's always some final tweaking of things like camera frame rates," says Blome.
The project at the paper mill was driven by the regulatory requirement to monitor loading and unloading of freight cars. The paper mill system uses three networks to monitor an indoor boiler and turbine, a railcar loading/unloading facility and a remote conveyor system. With the existing hard-wired cameras, nine images are tiled on a 70-in. display in the control room.
"Some of the existing hardwired cameras are losing their images and the conduit is corroding," says Mitch Jones, account manager at Emerson's local business partner R.E. Mason, the system integrator on the job. "So now if an existing camera goes out, a wireless one goes in." There's also bandwidth to add additional cameras where needed.
Adding the additional cameras to the existing wired network would have cost $89,000; the wireless system cost $46,000 for an estimated cost savings of 48%. The savings come from conduit, wiring and labor costs. "Most projects save more," said Jones. "Going wireless typically saves 50% to 75% of the installed cost."
